9076
J. Org. Chem. 1997, 62, 9076-9082
Synthesis of Substituted Bicyclo[2.2.2]octatrienes Michael W. Wagaman, Erika Bellmann, Miche`le Cucullu, and Robert H. Grubbs* Arnold and Mabel Beckman Laboratory of Chemical Synthesis, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125 Received June 10, 1997X
An efficient route to bicyclo[2.2.2]octatriene, barrelene, and substituted versions of this molecule has been developed starting from the benzene equivalent cis-3,5-cyclohexadiene-1,2-diol. Following the Diels-Alder reaction of this molecule with an activated acetylene, conversion of the diol to the final olefin was accomplished through formation of a thiocarbonate intermediate and subsequent reaction with 1,3-dimethyl-2-phenyl-1,3,2-diazaphospholidine (DPD). The synthesis developed allows a variety of barrelenes to be prepared in as few as three steps from commercially available starting materials. Introduction Since the synthesis of bicyclo[2.2.2]octatriene, barrelene, was first reported by Zimmerman,1,2 there has been considerable interest in the synthesis and study of this compound and its derivatives.3 Several syntheses of barrelene have been subsequently reported that allow this compound to be prepared by shorter routes than the original procedure.4-10 These routes have generally not been applied to the synthesis of substituted barrelenes, however. Conversely, methods employed for the synthesis of substituted barrelenes11-20 have generally not been applied to the synthesis of unsubstituted barrelene.21 One reason for this is that barrelenes such as dicyano- and bis(trifluoromethyl)barrelene are synthesized by the Diels-Alder reaction of highly activated acetylenes, dicyanoacetylene and hexafluoro-2-butyne, with benzene.11-13,15 This same procedure has not been used X Abstract published in Advance ACS Abstracts, December 1, 1997. (1) Zimmerman, H. E.; Paufler, R. M. J. Am. Chem. Soc. 1960, 82, 1514. (2) Zimmerman, H. E.; Grunewald, G. L.; Paufler, R. M.; Sherwin, M. A. J. Am. Chem. Soc. 1969, 91, 2330. (3) Zimmerman, H. E.; Armesto, D. Chem. Rev. (Washington, D.C.) 1996, 96, 3065. (4) Dauben, W. G.; Rivers, G. T.; Twieg, R. J.; Zimmerman, W. T. J. Org. Chem. 1976, 41, 887. (5) Taylor, G. N. J. Org. Chem. 1972, 37, 2904. (6) Weitemeyer, C.; Preuss, T.; deMeijere, A. Chem. Ber. 1985, 118, 3993. (7) Jefford, C. W.; Wallace, T. W.; Acar, M. J. Org. Chem. 1977, 42, 1654. (8) Weitemeyer, C.; deMeijere, A. Angew. Chem., Int. Ed. Engl. 1976, 15, 5, 686. (9) Cossu, S.; Battaggia, S.; DeLucchi, O. J. Org. Chem. 1997, 62, 4162. (10) Lightner, D. A.; Paquette, L. A.; Chayangkoon, P.; Lin, H. S.; Peterson, J. R. J. Org. Chem. 1988, 53, 1969. (11) Liu, R. H.; Krespan, C. G. J. Org. Chem. 1969, 34, 1271. (12) Liu, R. S. H. J. Am. Chem. Soc. 1968, 90, 215. (13) Krespan, C. G.; McKusick, B. C.; Cairns, T. L. J. Am. Chem. Soc. 1961, 83, 3428. (14) Kopach, M. E.; Harman, W. D. Abstr. Pap. Am. Chem. Soc. 1994, 208, ORGN 289. (15) Ciganeck, E. Tetrahedron Lett. 1967, 34, 3321. (16) Beerli, R.; Rebek, J. Tetrahedron Lett. 1995, 36, 1813. (17) Stapersma, J.; Rood, I. D. C.; Klumpp, G. W. Tetrahedron 1982, 18, 191. (18) Gompper, R.; Etzbach, K. H. Angew. Chem., Int. Ed. Engl. 1978, 17, 7, 603. (19) LeGoff, E.; LaCount, R. B. Tetrahedron Lett. 1967, 24, 2333. (20) Noble, K. L.; Hopf, H.; Jones, M.; Kammula, S. L. Angew. Chem., Int. Ed. Engl. 1978, 17, 602. (21) Reference 17 descibes a procedue for the synthesis of unsubstituted barrelene and substituted barrelenes in 3-8% yield. The procedure described in ref 18 allows the synthesis of ether-substituted barrelene by a route similar to that used for the synthesis of unsubstituted barrelene from bicyclo[2.2.2]oct-7-ene-2,5-dione.6,7,8,10
S0022-3263(97)01039-6 CCC: $14.00
to prepare unsubstituted barrelene since acetylene is not sufficiently activated to undergo an efficient Diels-Alder reaction with benzene. In fact, while dicyanobarrelene15 is obtained in 63% yield by this procedure, bis(trifluoromethyl)barrelene11-13 is produced in yields of only 8-10%.22 Following this trend further, Diels-Alder addition of the less activated, diester-substituted acetylenes to benzene produces barrelene products only when the benzene derivative employed is also activated.20,23,24
Recently, we reported the synthesis of 2,3-diestersubstituted barrelenes and the ring-opening metathesis polymerization (ROMP) of these molecules.25 We now report that the synthesis developed for those barrelenes can be extended to the synthesis of unsubstituted barrelene and other disubstituted barrelenes. Since benzene is a poor diene for most dienophiles, we employed cis3,5-cyclohexadiene-1,2-diol, or a protected form of this molecule, as a benzene equivalent. The route developed allows the preparation of a variety of barrelenes in as few as three steps from commercially available starting materials. Results and Discussion All syntheses were carried out in a similar manner with the Diels-Alder addition of an acetylene bearing electron-withdrawing groups to the benzene equivalent cis-3,5-cyclohexadiene-1,2-diol, 1, or the acetonide-protected form of this molecule, 9. The barrelenes were then obtained by conversion of the diol to the olefin. In cases where protection of the diol was not necessary, the DielsAlder reaction was followed by conversion of the diol, 3, to the thiocarbonate, 4, using (thiocarbonyl)diimidazole (TCDI) as shown in Scheme 1. Conversion of 4 to barrelene was then accomplished using 1,3-dimethyl-2phenyl-1,3,2-diazaphospholidine (DPD).26,27 In the case (22) Dicyanoacetylene and hexafluoro-2-butyne both produce higher yields of barrelene products when reacted with more active, substituted benzenes.11,13,15 (23) Magnussen, A.; Hansen, H. J. Helv. Chim. Acta 1997, 80, 545. (24) Truesdale, E. A.; Cram, D. J. J. Am. Chem. Soc. 1973, 95, 5825. (25) Wagaman, M. W.; Grubbs, R. H. Macromolecules 1997, 30, 3978. (26) Corey, E. J.; Carey, F. A.; Winter, R. A. E. J. Am. Chem. Soc. 1965, 87, 934.
© 1997 American Chemical Society
Synthesis of Substituted Bicyclo[2.2.2]octatrienes
J. Org. Chem., Vol. 62, No. 26, 1997 9077 Scheme 1
of 5d, the product is volatile and can be obtained in pure form by vacuum transferring it out of the reaction mixture. Purification of 5a-c can be accomplished by column chromatography or by a combination of column chromatography and recrystallization.25,27 Other methods to generate the final double bond either directly from the diol28,29 or by base-initiated thermal fragmentation of the benzaldehyde acetal as previously reported for benzobarrelene30,31 failed. Fragmentation of the acetal using KDA led to complete decomposition of the starting material, and as previously observed for the synthesis of benzobarrelene, no reaction occurred when LDA was employed. In the case of direct reduction of the diol, only decomposition was observed when Ti0 reagents were employed,29 and the method reported by Barua et al.28 produced only recovered starting material. An attempt to convert 4d to 5d using Ni(COD)232 resulted in complete consumption of the starting material but yielded none of the desired product. While the synthesis of 3a-d was readily accomplished by direct reaction of an activated acetylene, 2, with the unprotected diol, 1, the synthesis of several other barrelenes was greatly improved by using a protected form of the diol, 9. Using the acetonide has the dual advantage of protecting the diol from acid-catalyzed decomposition to phenol and also activating the diene so that less reactive dienophiles react more efficiently.33-35 Protection of the diol by thiocarbonate was also attempted, but rapid exothermic decomposition occurred when either TCDI or thiophosgene27 was employed. (27) Corey, E. J.; Hopkins, P. B. Tetrahedron Lett. 1982, 23, 1979. (28) Barua, N. C.; Sharma, R. P. Tetrahedron Lett. 1982, 23, 1365. (29) McMurry, J. E.; Fleming, M. P. J. Org. Chem. 1976, 41, 896. (30) Pu, L.; Grubbs, R. H. J. Org. Chem. 1994, 59, 1351. (31) Pu, L.; Wagaman, M. W.; Grubbs, R. H. Macromolecules 1996, 29, 9, 1138. (32) Semmelhack, M. F.; Stauffer, R. D. Tetrahedron Lett. 1973, 29, 2667. (33) Pittol, C. A.; Pryce, R. J.; Roberts, S. M. J. Chem. Soc., Perkin Trans. 1 1989, 1160. (34) Mahon, M. F.; Molloy, K.; Pittol, C. A.; Pryce, R. J.; Roberts, S. M.; Ryback, G.; Sik, V.; Williams, J. O.; Winders, J. A. J. Chem. Soc., Perkin Trans. 1 1991, 1255. (35) Cotterill, I. C.; Roberts, S. M.; Williams, J. O. J. Chem. Soc., Chem. Commun. 1988, 1628. (36) Jeanneaux, F.; Santini, G.; LeBlanc, M.; Cambon, A.; Reiss, J. G. Tetrahedron 1974, 30, 4197.
Scheme 2
To prepare a barrelene bearing a perfluorooctyl chain, the acetylene, 8,36-38 was first synthesized as shown in Scheme 2, and this was then reacted with the acetal, 9, as shown in Scheme 3. Use of 9 yielded the Diels-Alder adduct, 10, in near-quantitative yield in contrast to the reaction with 1, which resulted in decomposition to phenol, presumably due to the presence of residual hydrofluoric acid in 8.39 The acetonide protecting group was then removed under acidic conditions to yield the diol, 11, in quantitative yield. To optimize the ease of performing and purifying this reaction and minimize reaction time, several deprotection methods were tested. The fastest conversion was achieved using the dimethyl acetal, 10a, and a 1:1 mixture of 6 M HCl and dioxane. These conditions work well since the acetone generated boils off quickly, thus driving the reaction toward products. Methanol and pyridinium p-toluenesulfonate gave 11 in good yields, but these conditions required longer reaction times and periodic replenishment of methanol, which boiled off with the 2,2-dimethoxypropane produced. Deprotection of the benzaldehyde acetal, 10b, required much longer reaction times since the benzaldehyde or benzaldehyde dimethyl acetal produced is much less volatile than the products of deprotection of 10a. After the deprotection was complete, 11 was converted to barrelene 13 through the thiocarbonate, 12. Synthesis of unsubstituted barrelene and octylbarrelene also required use of the protected diol, 9a. The (37) Haszeldine, R. N. J. Chem. Soc. 1952, 2504. (38) Hudlicky, M. J. Fluorine Chem. 1981, 18, 383. (39) Further evidence for hydrofluoric acid present in compound 8, which is a liquid, was the ability of the neat liquid to etch glass when left in contact for extended periods. Because the acetonide, 9a, is deprotected by acid, the success of the reaction of 8 with 9a probably also relies on the fact that this Diels-Alder reaction is much faster than the reaction of 8 with 1.
9078 J. Org. Chem., Vol. 62, No. 26, 1997
Wagaman et al. Scheme 3
Scheme 4
acetylenes 14a,b,40,41 activated by a p-toluenesulfone group, underwent the Diels-Alder reaction with 9a as shown in Scheme 4. After the p-toluenesulfone group was removed by reductive desulfonylation,42 the diol was deprotected under acidic conditions as before, but in this case methanol and pyridinium p-toluenesulfonate were employed since the use of HCl resulted in decomposition. Using methanol was also an advantage since 17a is rather soluble in water and is difficult to extract from the aqueous HCl. Formation of the final olefin bond was accomplished as previously described. Attempts to synthesize a monoester-substituted barrelene by this route did not succeed. Starting from 9a and methyl propiolate, the diol, 20, was prepared by using the same procedure as for 17. This intermediate, which was more heat sensitive than the other diols, was converted into the thiocarbonate, 21, using thiophosgene and DMAP at 0 °C as shown in Scheme 5. Reaction of 21 with DPD under the same conditions employed for the other thiocarbonates produced only polymeric products, presumably by reaction of the acrylate functionality. Conclusions The synthesis presented here affords an efficient route to several substituted barrelenes in as few as three steps (40) Back, T. G.; Collins, S.; Kerr, R. G. J. Org. Chem. 1983, 48, 3077. (41) Waykole, L.; Paquette, L. A. Org. Synth. 1989, 67, 149. (42) Ku¨nzer, H.; Stahnke, M.; Sauer, G.; Weichert, R. Tetrahedron Lett. 1991, 32, 1949. (43) Boyd, D. R.; Sharma, N. D.; Barr, S. A.; Dalton, H.; Chima, J.; Whited, G.; Seemayer, R. J. Am. Chem. Soc. 1994, 116, 1147.
Scheme 5
from commercially available starting materials, as well as a route to unsubstituted barrelene. Reaction of activated acetylenes with cis-3,5-cyclohexadiene-1,2-diol or a protected form of this benzene equivalent generally afforded the Diels-Alder adduct in high yield. This intermediate was then converted to barrelene by formation of the thiocarbonate followed by elimination of this moiety to yield the final olefin bond. In addition to the barrelenes synthesized here, the route presented should allow the preparation of other related barrelenes and benzobarrelenes by using other dienophiles and/or any of the wide variety of substituted benzene equivalents similar to 1.43 We are currently exploring this possibility as well as the ring-opening metathesis polymerization of the compounds reported here.
Experimental Section General Procedures. NMR spectra were recorded on a QE Plus-300 MHz (300.1 MHz 1H; 75.49 MHz 13C) spectrometer or a JEOL JNM-GX400 (399.78 MHz 1H, 100.53 MHz 13C,
Synthesis of Substituted Bicyclo[2.2.2]octatrienes 376.14 MHz 19F) spectrometer as noted. Argon was purified by passage through columns of BASF R3-11 catalyst (Chemalog) and 4 Å molecular sieves (Linde). Elemental analyses were performed by Caltech Analytical Labs or Mid-West Microlab. High-resolution mass spectra were obtained from UC Riverside Mass Spectrometry Facility. Materials. THF and toluene were dried by passing through activated alumina columns. Acetylenes 2c44 and 14a,b40,41 and protected diols 9a,b30,31,35 were prepared according to literature procedures. Hexamethylphosphoramide (HMPA) was purchased from Aldrich and dried over calcium hydride and then distilled under reduced pressure prior to use. 3,3,3-Trifluoropropyne was purchased from PCR Inc. cis-3,5-Cyclohexadiene-1,2-diol was obtained from ICI. (Thiocarbonyl)diimidazole (TCDI), 1,3-dimethyl-2-phenyl-1,3,2-diazaphospholidine (DPD), 2,2-dimethoxypropane, perfluorooctyliodide, pyridinium p-toluenesulfonate (PPTS), methyl propiolate, 2-ethylhexanol, acetylenedicarboxylic acid, hexafluoro-2-butyne, and SmI2 in THF were purchased from Aldrich and used without further purification except where noted otherwise. Compounds 3a,b-5a,b were prepared as previously reported.25 Bis(2-ethylhexyl) 2,3-Dihydroxy-5,7-bicyclo[2.2.2]octa5,7-diene-5,6-dicarboxylate (3c). A 100 mL round-bottom flask was charged with 10.43 g (30.81 mmol) of 2-ethylhexyl acetylenedicarboxylate and 15.00 g (150 mmol) of CaCO3. After the mixture was stirred for 30 min under a flow of argon, 1.73 g (15.43 mmol) of cis-3,5-cyclohexadiene-1,2-diol and 2.13 mL of dry THF were added to the flask. The reaction was heated at 60 °C for 3 days and then filtered to remove CaCO3. After the CaCO3 was rinsed with CHCl3, the solvent was removed under vacuum to yield a yellow oil. The yellow oil was loaded onto a column of silica gel and eluted with 10% ethyl acetate/hexane. Following removal of solvent, 5.03 g (11.16 mmol, 71.20%) of a mixture of syn and anti product isomers was obtained as a yellow oil. Note: Calcium carbonate was added to this reaction to decrease formation of phenol: 1H NMR (300 MHz, C D ) anti δ 6.21 (m, 2H), syn δ 5.72 (dd, 6 6 J ) 4.2, 3.3 Hz, 2H), 4.21 (m, 2H) 4.19-4.02 (m, 6H), 3.73 (bs, 2H), 2.37 (bs, 2H), 1.53 (m, 2H), 1.40-1.02 (m, 16H) 0.890.79 (m, 12H); 13C NMR (75 MHz, C6D6) anti δ 166.1, 141.0, 132.3, 68.5, 67.8, 47.9, 39.5, 31.1, 29.6, 24.5, 23.7, 14.6, 11.5; syn δ 167.35, 140.3, 132.4, 68.3, 67.2, 47.3, 39.5, 31.1, 29.6, 24.5, 23.7, 14.6, 11.5; HRMS calcd for C26H42O6 (M + H)+ 451.30594, found 451.3070. Anal. Calcd for C26H42O6: C, 69.30; H, 9.39. Found: C, 68.91; H, 9.34. Bis(2-ethylhexyl) 2,3-(Thiomethylenedioxy)-5,7-bicyclo[2.2.2]octa-5,7-diene-5,6-dicarboxylate (4c). Compound 3c (3.98 g, 8.84 mmol) and 1.93 g (90% pure, 9.72 mmol) of (thiocarbonyl)diimidazole (TCDI) were loaded into a 50 mL flask purged with argon. Dry toluene (30 mL) was added to yield a solution containing undissolved TCDI. The solution was heated in an oil bath, which had been preheated to 135 °C, for 20 min. An additional 0.913 g of TCDI was loaded into the flask and the reaction was heated for 15 min. After cooling to room temperature, the yellow solution was poured onto a plug of silica gel and eluted with 50% ethyl acetate/hexane. Removal of solvent under vacuum yielded 4.01 g (8.15 mmol, 92.12%) of 4c as a yellow oil: 1H NMR (300 MHz, CDCl3) anti δ 6.55 (dd, J ) 4.2, 3.3 Hz, 2H), 5.00 (m, 2H), 4.55 (m, 2H), 4.12 (m, 4H), 1.60 (m, 2H), 1.4-1.29 (m, 16H), 0.90 (t, J ) 7.2, 12H); syn δ 6.40 (dd, J ) 4.5, 3.0 Hz, 2H), 4.91 (m, 2H), 4.55 (m, 2H), 4.14 (m, 4H), 1.64 (m, 2H), 1.46-1.23 (m, 16H), 0.90 (m, 12H); 13C NMR (75 MHz, CDCl3) anti δ 191.5, 164.3, 139.4, 131.3 81.4, 69.1, 43.0, 38.9, 30.8, 29.1, 24.0, 23.9, 14.3, 11.1; syn δ 191.6, 165.5, 139.6, 132.4, 80.7, 68.5, 43.4, 39.6, 31.0, 29.7, 24.4, 23.8, 14.6, 11.6; HRMS calcd for C27H40O6S (M + H)+ 493.2624, found 493.2620. Anal. Calcd for C27H40O6S: C, 65.82; H, 8.18. Found: C, 65.87; H, 8.21. Bis(2-ethylhexyl) Bicyclo[2.2.2]octa-2,5,7-triene-2,3-dicarboxylate (5c). A 50 mL round-bottom flask was charged with 4.013 g (8.15 mmol) of compound 4c and 4.50 mL of 1,3dimethyl-2-phenyl-1,3,2-diazaphospholidine (DPD) to yield a (44) Jeffery, G. H.; Vogel, A. I. J. Chem. Soc. 1948, 674. Acetylene 2c was purified on silica gel (10% ethyl acetate/hexane) rather than by distillation.
J. Org. Chem., Vol. 62, No. 26, 1997 9079 brown mixture. The mixture was heated under argon in an oil bath at 40 °C for 7 days. The brown solution was then loaded onto a silica gel column and eluted with 10% ethyl acetate/hexane. After evaporation of solvent, 1.78 g (4.27 mmol, 52.5%) of the product was obtained as a yellow oil: 1H NMR (300 MHz, CDCl3) δ 6.87 (m, 4H), 5.08 (m, 2H), 4.06 (dd, J ) 6.0, 3.0 Hz, 4H), 1.59 (m, 2H), 1.39-1.28 (m, 16H), 0.88 (m, 12H); 13C NMR (75 MHz, C6D6) δ 167.5, 149.7, 140.9, 68.2, 50.7, 39.5, 31.1, 29.6, 24.5, 23.7, 14.6, 11.5; HRMS calcd for C26H40O4 M+ 416.2926, found 416.2920. Anal. Calcd for C26H40O4: C, 74.95; H, 9.68. Found: C, 74.87; H, 9.86. 5,6-Bis(trifluoromethyl)bicyclo[2.2.2]octa-5,7-diene2,3-diol (3d). A Fischer-Porter bottle was charged with 9.16 g of cis-3,5-cyclohexadiene-1,2-diol (81.7 mmol) and purged with argon. Dry THF (40 mL) was then added to yield a colorless solution. The flask was then closed and pressurized to 65 psi with hexafluoro-2-butyne. As the pressure slowly decreased, more gas was admitted to maintain the initial pressure. After 1 week, the pressure was released, and solvent was removed by rotary evaporator to yield the product as 21 g (76.6 mmol, 94%) of a white solid. The crude product, which appeared clean by 1H NMR, was used in the next reaction without further purification: 1H NMR (300 MHz, CDCl3) anti δ 6.50 (m, 2 H), 4.23 (br s, 2 H), 3.87 (br s, 2 H), 2.65 (br s 2 H); syn δ 6.32 (m, 2 H), 4.21 (m 2 H), 3.85 (br s, 2 H), 3.15 (br s, 2 H); 13C NMR (75 MHz, CDCl3) anti δ 139.95m, 131.46, 120.94 (q, J ) 275.47 Hz), 66.45, 45.19; syn δ 137.14m, 131.91, 121.22 (q, J ) 272.60 Hz), 65.75, 45.03; 19F NMR (376 MHz, CDCl3) anti δ -61.49 s; syn δ -61.24 s; HRMS calcd for C10H12F6NO2 (M + NH4+) 292.0769, found 292.0775. Anal. Calcd for C9H12F6O2: C, 43.81; H, 2.94; F, 41.58. Found: C, 44.03; H, 3.07; F, 41.75. 5,6-Bis(trifluoromethyl)bicyclo[2.2.2]octa-5,7-diene2,3-thiocarbonate (4d). 3d (10.01 g, 36.5 mmol) and 7.53 g (90% pure, 38.0 mmol) of TCDI were put in a 500 mL roundbottom flask, and 150 mL of dry toluene was added. The flask was then put in an oil bath preheated to 130 °C. After 30 min, the reaction was cooled to rt and poured into a separatory funnel containing 10 mL of 1 M HCl. The aqueous layer was extracted with 3 × 100 mL ether. All organic layers were combined and dried over magnesium sulfate. After removal of solvent under vacuum, the product was obtained as a brown solid. This was dissolved in 100 mL of ethyl acetate, and 50 g of silica gel was added. Following evaporation of the solvent under vacuum, the free-flowing solid was loaded onto a column containing 750 g of silica gel and eluted with 20% ethyl acetate/ hexane and then 50% ethyl acetate/hexane. The product was obtained as two isomers (total ) 9.91 g, 31.33 mmol, 86%). The major isomer, anti (identified by comparison to similar previously characterized compounds25), was a white powder, and the minor isomer, syn, was a slightly yellow crystalline solid: 1H NMR (300 MHz, CDCl3) anti δ 6.61 (m, 2H), 4.98 (m, 2H), 4.61 (m, 2H); syn δ 6.50 (m, 2H), 4.97 (br s, 2H), 4.64 (m, 2H); 13C (75 MHz, CDCl3) anti δ 190.57, 137.28 m, 131.12, 120.17 (q, J ) 272.1 Hz), 80.26, 41.631; syn δ 190.24, 137.01 m, 132.09, 120.36 (q, J ) 273.95 Hz), 79.86, 41.54; 19F NMR (376 MHz, CDCl3) anti δ -61.47 s; syn δ -61.22 s; HRMS calcd for C11H6F6O2S 315.99673, found 315.9985. Anal. Calcd for C11H6F6O2S: C, 41.78; H, 1.91, F, 36.05. Found: C, 41.82; H, 1.96; F, 36.13. 2,3-Bis(trifluoromethyl)bicyclo[2.2.2]octa-2,5,7triene (5d). A 450 mL Schlenk flask was loaded with 4.336 g (13.7 mmol) of 4d and evacuated and then backfilled with argon three times. Next, 7.81 mL (97% pure, 41.1 mmol) of DPD, which was pumped down to 60 mTorr to remove volatile components, was added. This yielded a wet mixture, but most of the solid did not dissolve. The reaction was heated in an oil bath at 45 °C for 3 days. The flask was vented periodically to allow CO2 formed by the reaction to escape. After being cooled to rt, the product was vacuum transferred out of the reaction mixture into a Schlenk flask in liquid nitrogen. A second vacuum transfer yielded 2.078 g (8.65 mmol, 63%) of the desired product as a clear colorless liquid: 1H NMR (300 MHz, CDCl3) δ 6.90 (m, 4 H), 5.092 (m, 2 H); 13C NMR (75 MHz, CDCl3) δ 145.18 m, 139.85, 122.07 (q, J ) 272.07 Hz), 47.92; 19F NMR (376 MHz, CDCl3) δ -61.73 s; HRMS calcd
9080 J. Org. Chem., Vol. 62, No. 26, 1997 for C10H6F6 240.0372, found 240.0381. Anal. Calcd for C10H6F6: C, 50.02; H, 2.52; F, 47.47. Found: C, 49.89; H, 2.48; F, 47.21. 1-Iodo-1-(trifluoromethyl)-2-(perfluorooctyl)ethylene (7). Under argon, 23.75 g (43.5 mmol) of perfluorooctyl iodide was loaded into a steel bomb, and the bomb was then sealed and cooled to -78 °C. Approximately 4.8 g (51.0 mmol) of trifluoropropyne was condensed into the reaction vessel, which was then sealed and warmed to rt; the pressure increased to 100 psi. The reaction was then heated for 24 h at 210 °C. The pressure initially increased to ∼250 psi and then gradually decreased to
